I think wearing them together works so well because the extremities of the differences in these colors creates a "happy medium". When making first impressions, we want to have the "happy medium" so we can appear to be the right fit for whatever a company, significant other or even a friend is looking for.

For example, when going on several interviews, you may have many on the same day and do not have time to cater your looks specifically to each company so you need to wear something that fits with every company. By wearing black and white, you're covering the basics that just about every company is looking for. One could be someone that wants to be a leader (black) but understands they need to grow with the company first (white).